In the field of internal combustion engine, various technologies for improving the fuel efficiency by decreasing the pumping loss are known. For example, an internal combustion engine disclosed in JP-A-2002-070597 comprises an intake operating angle changing mechanism for changing the operating angle of an intake valve; and a phase changing mechanism for changing the center phase of the operating angle of intake and exhaust valves. Also, in an middle-load range of the internal combustion engine, the decrease in the pumping loss, and the improvement in the fuel efficiency, and the improvement in the exhaust gas purification performance are sought by setting up the predetermined amount of a minus overlap period (a non-overlap period) at the middle-load range of the internal combustion engine and by leaving a combusted gas in a combustion chamber (namely, an internal EGR <Exhaust G as Recirculation>). Further, when the load is shifted from the middle-load range to an extremely low-load range of the engine, the stability of combustion is improved in the extremely low-load range such as an idle state, etc. by advancing the opening timing of the intake valve to the intake top dead center and retarding the closing timing of the exhaust valve to the intake top dead center in order to eliminate the minus overlap period.
In addition, an internal combustion engine disclosed in JP-A-11-117777 comprises a variable valve mechanism control means for controlling a variable valve mechanism including intake and exhaust valves; and a throttle valve for controlling the amount of intake air according to the depressed amount of an accelerator. Also, when the internal combustion engine is in the low-load or middle-load range, the pumping loss is decreased by controlling the throttle valve to be almost fully opened regardless of the depressed amount of the accelerator, and the amount of intake air is controlled by controlling the closing timing and the lift amount of the intake valve.
The internal combustion engine disclosed in JP-A-2002-070597 decreases the pumping loss by the internal EGR, but it does not consider to decrease the pumping loss by throttling intake air by a throttle valve. Also, the internal combustion engine disclosed in JP-A-11-117777 decreases the pumping loss by quickly closing the intake valve, but does not consider to decrease the pumping loss by controlling the amount of burned gas left in the combustion chamber due to the internal EGR.
Further, during warming-up of an internal combustion engine whose temperature is low, its combustibility is lower than that of the engine which is already warmed up since the temperature in the combustion chamber is also low and thus the evaporated status of fuel is poor. Therefore, if the internal EGR rate is high, the combustion becomes more unstable such that an accidental fire could easily occur. Moreover, because the internal EGR is performed to lower the maximum combustion temperature, the warming-up of the internal combustion engine is not promoted.